agent-tui is currently built and shipped using the assisted-installer-agent repo. Since it will be move into its own repository (agent-installer-utils), it's necessary to cleanup the previous code.

• Remove agent-tui and nmstate dependencies from Docker image (https://github.com/openshift/assisted-installer-agent/blob/master/Dockerfile.ocp)
• Remove source (and vendored code) (https://github.com/openshift/assisted-installer-agent/tree/master/src/agent_tui)